Electric pulse signalling system having switching means connected to a constant-voltage source



Feb. 8, 1966 H. J. WARD ETAL ELECTRIC PULSE SIGNALLING SYSTEM HAVINGSWITCHING MEANS CONNECTED TO A CONSTANT VOLTAGE SOURCE Filed Dec. 8,1959 4 Sheets-Sheet 1 J l x o S a, Z 8 Ha Mi. l l v 5 g 5 l g; S Q) m gis v v 5l 1' T vwv-lnr S x s Q Q) I) m f{ Y I I U Q a 1 1 u E n 0% g JINVENTORS. U HUGH J. NARC 2 BY ERNEST M EUNOY s i WCM- Q AGENT Feb. 8,1966 H. J. WARD ETAL 3,234,514

ELECTRIC PULSE SIGNALLING SYSTEM HAVING SWITCHING MEANS CONNECTED TO ACONSTANT VOLTAGE SOURCE Filed Dec. 8, 1959 4 Sheets-Sheet 2 x S S T 5; Aa 1 r f S &|- J, 5|-

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INVENTORS.

LINEv HUGH d. wA/Qo BY ERNEST MBU/VOY w wze AGENT Feb. 8, 1966 H. J.WARD ETAL ELECTRIC PULSE SIGNALLING SYSTEM HAVING SWITCHING MEANSCONNECTED TO A CONSTANT VOLTAGE SOURCE Filed Dec. 8, 1959 4 Sheets-Sheet5 PERU/ON OF FEM OF cigrK/Qo COND/T/O/V OF FEM DUP/NG TRANSM/TTER 7M5PER/OD NQ 50/ 3 (ASSUMEQ) 7 RELAYS sxsx,ss,sw 77 7- 7 222 333444555 5wsm/vps ON 0 CONTACT FHA) SP A RELAYS/V 5/0 cow/70mm Z 77, V

//v FORM/1 T/O/V SEA/7 o o 2 2 3 3 4 4 RELAT/NG 7'0 co/vmcr 1 F/RSTCHANGE SECOND CHANGE /i7// 17/ Inventors Attorney Feb. 8, 1966 H. J.WARD ETAL 3,234,514

ELECTRIC PULSE SIGNALLING SYSTEM HAVING SWITCHING MEANS CONNECTED TO ACONSTANT VOLTAGE SOURCE Filed Dec. 8, 1959 4 Sheets-Sheet 4 lTEM OCOND/T/ON OF FEM DUR/NG 0/ 234567 BQ/OI/AZUM/S SIG CO/VDFf 7 FROM AC0 7j 7 WFORMA 770/V PE C E l ED RELAT/NG 7'0 CONTACT F/RST CHANGE SECONDCHANGE A m/ 7/7 RELAY CR 7/'- 7 7 RELAYS cY, cx 7 RELAY CP 7 7 W RELAYc/v RELAY cc; V/// DR/VE MAGNET CW 7 W 7 7- RELAY CIA 17 Inventors'H.J.WARD-E. .BU DY A Home y United States Patent O 3,234,514 ELECTRICPULSE SIGNALLING SYSTEM HAVING SWITCHING NIEANS CONNECTED TO A CON-STANT-VOLTAGE SOURGE Hugh lennings Ward and Ernest Mark Bundy, Aldwych,London, England, assignors to International Standard ElectricCorporation, New York, N. Y.

Filed Dec. 8, 1959, Ser. No. 858,143 Claims priority, application GreatBritain, Dec. 12, 1958, 40,170/58 12 Claims. (Cl. 340-147) Thisinvention relates to electrical signalling systems with particularreference to their use in remote control and supervisory systems.

In remote control and supervisory systems it is frequently desirable 'totransmit two signals representing, respectively, the idle and theWorking conditions of a unit of apparatus. It is common-practice totransmit over one line a succession of such signals, each successivesignal referring to a different apparatus unit. In order that the signalrelating to a particular apparatus unit may be directed .to the desiredapparatus unit in the .case of a remote control system, or tosupervisory equipment corresponding thereto in the case of a remotesupervisory systern, it .is necessary that each individual signal shouldbe separately identifiable. A common method of identifying these signalsis with reference to their numerical position in. a succession ofsignals, e. g., by arranging that the fourth signal of a successionrelates to the fourth'apparatus unit controlled or supervised. A knownmethod of meeting these requirements is to connect a control and aremote station by a pair of conductors; to connect a battery across theconductors in one sense to provide one of the signalling conditions,e.g., apparatus unitidle; to connect the battery across the conductorsin the opposite sense to'provide the other signalling condition, e.g.,apparatus unit working; and to disconnect the battery from theconductors between successive signals. That is to say three lineconditions, which for simplicity may be referred to as positive,negative and zero, arerequired for the transmission of therequisiteinformation.

Difiiculty arises-when the conductors are replaced, in Whole orpart, bya voice frequency telegraph system, as a signalling channel in such asystem can generally assume only .two states and one of theseis assumedcontinuously when'the channel is inoperative. When such a voicefrequency system is introduced between a control and a remote station,either of two known arrangements maybe used. Firstly, two voicefrequency'channels maybe provided, in which case a positive condition isrepresented by the transmission of signalling toneover the firstchannel, negative by the transmission of signalling tone over the secondchannel, and zero by the inoperative tone on both channelssimultaneously. Secondly, only one voice frequency channel may be used,in which case positive may be represented by a shortpulse of signallingtone on the channel, and negative by a long pulse of signalling tone.The second arrangement suffers from the obvious disadvantage that thespeed of transmission of information with such a system is inevitablyslower than with two channels and that the delay will vary in accordancewith the information transmitted. It is an object of the presentinvention to overcome .this disadvantage without having to provide asecond voice-frequency channel, i.e., by using only two signallingconditions.

According to the invention there is provided a method of electricsignalling between a transmitter and a-receiver which employs twoalternative signalling conditions and in which a signal includes aninformation time period during which either signalling condition may betransmitted in accordance with information which it is desired totransmit and at least a first change in signalling conditions.

According to the invention there is also provided an electric signaltransmitter having change-over switching means capable of performing atleast a first change-over during a transmitted signal, and selectionswitching means operable to select for transmission during a signaleither of two alternative signalling conditions before said firstchange-over and the other signalling condition after said firstchangeeover.

According to the invention there is further provided an electricalsignal receiver having change-over switching means responsive to a.change from either to the other of two alternative received signallingconditions; two signal repeaters corresponding to the two signallingconditions, and each capable of selection to the exclusion of the otherby an operation of the change-over switching means; and energizing meansfor the repeaters arranged to operate a repeater which has beenselected.

The invention will now be described with reference to its application toa remote supervisory system, but it will be understood that the use ofthe signalling method to be described is not restricted to either remotecontrol or remote supervisory systems. Further, although suitable foruse over a single voice-frequency channel, the method may be used withany signalling channel which will trans mit at least two signallingconditions. In the following description the signalling channel isdescribed as a doublecurrent duplex earth-return channel. Alternatively,the signalling channel could be part of a radiolink.

Inthe description, reference will be made to the accompanying drawingsin which:

FIG. 1 shows the circuit arrangements at a control station.

'FIG. 2 shows circuit arrangements at a-remote station,

FIGS. 3, 4 are time charts showing the sequence of operations in thecircuits of FIGS. 1,2. For convenience, changes in signalling conditionsare shownin both charts.

The circuits shown in .FIGS. 1 and 2 contain a multivibrator with athird winding and a follower relay .(CY, CX in FIG. 1 and SY, SX in FIG.2) of the type having a resistance-capacitance network associatedtherewith. These multivibrators can asusrne two conditions which mayconveniently be designated mark and space, and it is a feature of themultivibrators that the time during which a vibrator remains in one ofthese conditions is adjustable independently of the time during which itremains in the alternative condition, i.e., that the mark and spaceconditions need not have equal durations. This feature is made use of inthe present invention.

OUTLINE OF OPERATION Throwing a control key (FIG. 1) at the controlstation initiates the operation of the multivibrator SY, SX (FIG. 2.) atthe remote station. At each cycle of operation of this multivibrator, auniselector SW steps once and tests an apparatus unit connected to oneof its bank contacts. Relays 3 SP, SN may or may not operate accordingto the state of the apparatus unit tested. Contacts sp3, m2 inconjunction with contact ss4 determine whether positive or negativebattery is applied to the point A, i.e., which of two alternativesignalling conditions is to be transmitted. The duplex signallingchannel identified in FIGS. 1, 2 as line is capable of assuming morethan two conditions during signalling. However, in order to show clearlythat the supervisory information is transmitted by the use of only twosignalling conditions, the signalling conditions will be described interms of the conditions applied to the point A. Contact ss4 is operatedby relay SS which, by its contact ssl, controls the stepping of theuniselector SW. The signalling conditions applied to point A aretherefore related in time to the stepping of the uniselector SW.Referring to the time charts of FIGS. 3, 4, it will be seen that whilethe uniselector SW stands on one contact, the signalling conditionapplied to a point A refers to the uniselector contact previouslytested.

As soon as the multivibrator SY, SX starts to operate, relay SS is alsooperated and contact ss4 changes over. At the control station, relay CR(FIG. 1) responds to this change-over and releases the multivibrator CY,CX which performs one cycle and comes to rest, causing a uniselector CWto step to and dwell on its first contact. As already explained, contactss4 changes over in this manner once in each cycle of the multivibratorSY, SX. At each such change over, the multivibrator CY, CX operatesonce, and the uniselector CW steps once. Once in each cycle of themultivibrator CY, CX, the signalling conditions applied at point A causeone or other of relays CP, CN to operate, which in turn cause thelighting or extinguishing of supervisory lamps at the control station.

Referring again to FIGS. 3, 4 the supervisory information is transmittedas a succession of signals, each of which refers to one apparatus unitwhich has been tested. For convenience of description, each such signalmay be divided into three equal time periods. At the end of the secondperiod of each signal, relay SS is operated, which both prepares theuniselector SW to step to its next bank contact and causes the relaycontact ss4 to change over. The

connections and operation of contacts sp3, snZ are such that thischange-over always produces a change in the signalling conditionsapplied to the point A. At the end of the third time period of a signal,the relay SS is released, the uniselector SW steps once and contact ss4-changes back. This may or may not produce a change of signallingconditions'at point A depending on the positions taken up by contactssp-3, sn2. The signalling conditions applied as a result of contact ss4moving back are maintained for the first two periods of the next signal.These two periods together constitute the information time period of thesignal. At the control station, the multivibrator, CY, CX starts a cycleof operation and the uniselector CW steps 'once, on the changeoverofcontact ss4 at the end of each second time period. As alreadyexplained, contact ss4 moves back at the end of each third time period.If, but only if, a change of signalling conditions results, the relay CRwill respond and contact crl will change over. The multivibrator CY, CXis adjusted, so that contact 0171 has time to operate before themultivibrator returns to mark. That is to say, the multi vibrator CY,CX. is adjusted to return to mark during the information time period ofa received signal. When the multivibrator CY, CX returns to mark,contact x1 closes causing either relay CP or CN to operate dependand afurther cycle of the multivibrator CY, CX is' initiated.

The system comprises a transmitter (FIG. 2)and a receiver (FIG. 1), inwhich three signalling conditions are transmitted and received withoutrequiring three signals of different amplitudes to indicate the threesignalling conditions.

The transmitter generates a transmission signal including at least oneinformation time period (for instance, time intervals 6, 7, and 8 ortime intervals 9, 10, and 11, FIGS. 3 and 4) having at least oneinformation signal portion and another information signal portion insequence. To produce this transmission signal the transmitter includes asource of voltage having two output terminals, one of the outputterminals providing a first voltage level, such as volts associated withcontact .9112 of relay SN and with contact SP3 of relay SP, and theother of the output terminals providing a second voltage level distinctfrom the first voltage level, such as +80 volts associated with contact.9112 of relay SN and with contact sp3 of relay SP.

The transmitter further comprises a first switching means includingrelay multivibrators SY, SX and their associated contacts and relay SSand its contact ss4. The cyclic operation of relay multivibrator SY, SXactivates and 'deactivates relay SS to cause contact ss4 to apply a -80voltage to point A in its unoperated condition through contact sp3 and a+80 voltage to point A in its operated condition through contact m2.Thus, the first switching means is selectively coupled to the two outputterminals of the voltage source to produce at the output (point A) ofthe first switching means at least a first change between the firstvoltage level and the second voltage level as the one information signalportion, this change between the two voltage levels being accomplishedupon activation of relay SS by relay multivibrator SY, SX.

In addition, the transmitter includes a second switching mean-s composedof relay SP and its contact sp3, relay SN and its contact m2, andstepping relay SW and the testing contacts associated therewith. Throughcontacts sp3 and sn2 the second switching means is selectively coupledto the two output terminals of the source of voltage by steppingrelaySW. The presence of an open or closed supervisory contact (SUP)selects one of the first and second voltage levels for coupling throughcontact ss4 to point A, the output of the first switching means asanother information signal portion.

Considering the operation of the transmitter during the time intervals9, 10, and 11, an information time period, relay multivibrator SY, SXwill be activated to place contacts syl and sxl in the S condition toactivate relay SS causing contact ss4 to move from contact sp3 to $112and, hence from 80 volts to a +80 volts. This operation provides in theone information signal portion a changeover between -80 volts to +80volts. Stepping relay SW will next test contact 3 and if it is assumedthat the supervisory contact SUPS is closed, relay SP and relay SN willbe operated causing contacts M2 and sp3 to assume their alternatepositions so that when relay SS is de activated by the reversal of theoperating condition of multivibrator SY, SX, contact ss4 will bereturned to its normal indicated position. However, since relays SP andSN have been activated, contact ss4 will be coupled through sp3 to +80volts whichwill maintain +80 volts at the output of the first switchingmeans (point A).

Considering now time intervals 6, 7, and 8 constituting anotherinformation time period. Relay multivibrator SY, SX will be activated toits S condition to activate relay SS, thereby causing contact ss4 tomove from the ilustrated position to its alternate position therebychanging from a 80 volts to a +80 volts due to contacts sp3 and m2 beingin their illustrated position. Upon the re.- turn of relay multivibratorSY, SX to its normal illustrated M condition, relay SS will bedeenergized and contact ss4 will return to its normalindicated position,thereby causing a second changeover, but this time from +80 volts to 80volts. This second changeover represents a third information portion ofthe information time period. Relays SP and SN will remain in theirunenergized condition in this information time periodsince-thesteppingrelay SW has landed-on a contactwhosesupervisory switch is intheopen condition and therebyprevents the energization of relays SN andSPand, thus, the another information signalaportion is selected as 80volts.

The information timev period of the transmission signal at point A istransmitted through a transmission medium indicated as LINE and .ispresented to the receiver of FIG. 1 which includes therein a thirdswitching means coupled to the transmission medium (LINE), includingrelayCR and its contact crl. This'third.switchingmeans is responsive tothe first change of the one information signal portion and the-selectedone of the first voltage level and second voltage level of anotherinformation signal portion of the transmission signal for operationthereof.

The receiver in accordance with this invention further includes twomeans, relay CP and its contact and relay CN and its contact, each oneof which represents one of the voltage'levels. For instance, relay CPrepresents the 80 voltage level and relay CN represents the +80 voltagelevel. These two means are coupled to the third switching means throughcontact 011 of the third switching means for exclusive selection of oneof the two means by the third switching means during theoperationthereof. The energizing means coupled to the third switchingmeans through contact cr1 includes the inhibit winding of relaymultivibratorCX, CY and their associated contacts cxl and cyl.

Considering now the operation of the receiver during the informationtime period including time intervals 9, and .11, the first change in thetransmission signal from 80 volts to +80 volts will cause activation ofrelay CR and movement of .its contact crl from the M to the S position,causing the relay multivibrator to be energized and to move itsassociated contacts from the M position to the S position to therebydeactivate the'inhibit'winding for a predetermined period. After thispredetermined period relay multivibrator CX, CY will return to its Mcondition thereby applying through contact 0x1 and the inhibit windingthe activating voltage to contact crl. Due to the fact that the signalbeing transmitted remains at +80 volts during time intervals 10 and 1-1,relay SR will remain energized and will hold contact er]; in its Scondition, thereby activating relay CN. Thus, relay CN is exclusivelyselected bythe third switching means to indicate the presence of +80volts in the another information portion.

Considering now the information time period including time intervals 6,7', and 8. A-first change of'voltage from a 80 volts to a +80 voltswillactivate relay CR and move its contact crl from the M position to the Sposition to activate relay multivibrator CX, CY for its cyclic operationby removing the inhibiting voltage present at contact 0x1 from theinhibit winding. Since a second change from a +80 volts to 80 voltsoccurs during these time intervals (third information portion) relay CRand relay multivibrator CX, CY will 'be deenergized and will return toits normal position and in effect will energize relay CP through theinhibit winding of relay multivibrator CX, CY and contact 0x1. Sinceduring time intervals 7 and 8 the voltage levels being sent from thetransmitter to the receiver is a -80 volts, relay CR will remainunenergized, contact cr1 will remain in its M condition and, hence,relay CP will remain selected or activated to indicate the presence of80 volts in the another information portion, this selection beingexclusively controlled by the third switching means.

6 DETAILED DESCRIPTION In the followingdescription, it will beconvenient to consider each signal as divided into three equal timeperiods. The multivibrator SY, SX at the remote station is arranged tohave amark-to-space ratio of 221; while the multivibrator CY, CX at thecontrol station, has a ratio of 1:2. These ratios, however,,are used fordescriptive purposes only, and in practice any suitable ratios could beused.

The signals will be described in connection with: the transmission ofsupervisory information from a remote station to a control station,thatis to say; with reference to the signalling conditions applied tothe-pointA (FIG. 2) for transmission to the control station. In theexample to be described, the transmission of information is controlledby the operation .of a controlkey at the-control station. When thecontrol key is operated, the resultingsignalv is transmitted tothe'remote station over .a dupleX channel (line) capablecf. transmittingsignals in both directions at the same time. However, if the signallingchannel connecting the two stations is capable of assuming only twosignalling condtiions, as is the case with a voice-frequencytelegraphsignalling channel, and if only one such channel isprovided,.it would be necessary to provide directional switchingequipment at each end ofthe channel so. that the channel could beworkedlfirst in an outward direction for transmitting the control signaland then in an inward-direction for transmitting the signals conveyingthe supervisory information. Such directional switching equipment iswell known in the artand will not be described here.

The apparatus at the remote station. includes a freerunningmultivibrator SY, SX arranged to start. inresponse to a suitablestarting signal, in this case the throwing of a control key at thecontrol. station. Also providedv is a uniselector SW which steps underthe, control, of the multivibrator SY, SX and tests each bank .contactwhile it dwells thereon. The condition of each bank contact isdetermined 'by whether a supervisory contact, connected thereto andindicative of the state of an apparatus unit to be supervised, is openor closed, e.g.,.the condition of bank contact 3 isdetermined by. theopen .or closed condition of supervisory contact SUP3, which, in turn,is determined by the conditionof an apparatus unit associated therewith.If the'contact SUP3 is closed when the uniselector SW steps onthebankcontact .3, relay SP will be energized fol-lowed by relay SN. .On theother. hand, if the contact SUP3 is open, neither relay will beenergized. Relays SP, SN respond to the condition .of each bankcontactinturn andiby means .of their contacts sp3, m2 determine, in conjunctionwith contact ss4, the signalling conditions appliedto the point.A. Whilethe uniselector SW stands on one bank contact, a signal relating to theprecedingbank contact is transmitted.

At the control station, a multivibrator CY, CX' operates on a start-stopbasis and .performs one cyclev for each cycle of the multivibrator SY,SX at the remote station. A uniselectorCW steps under the control of themultivibrator CY, CX. While .the uniselector CW is standing on, one bankcontact one of the relays. CP, CN is operated depending upon thesignalling condition applied to the point A in relation to thecorresponding bank. contact of the uniselector SW at the remote station.A red and a green supervisory lamp is. provided at the control stationfor each apparatus unit supervised at the remote station. In theexample, when a supervisory contact is open the corresponding green lampglows, and when the supervisory contact is closed the corresponding redlamp is lit and the green lamp is extinguished;

The interaction of the two multivibrators and of the relays anduniselectors associated therewith will be more easily understood byreferringto the time chart shown in FIGS. 3, 4 which also serves toillustrate the nature of the signals transmitted. For ease of reference,the op- 7 eration of the equipment will be described stage by stage in aseries of time periods numbered from upwards. In the example, a signalconsists of three successive time periods, e.g., 4, 5, 6. During theperiod 4, 5, 6 the uniselector SW stands on bank contact 2 while thesignal relatingto bank contact 1 is transmitted. During the first twoperiods 4, of this signal, the signalling conditions applied to thepoint A (FIG. 2) for transmission to the control station are determinedby which of two alternative conditions is extended over contact sp3 whencontact ss4 is restored. These periods 4, 5 together constitute aninformation time period during which the supervisory information 'frombank contact 1' of uniselector SW is transmitted to the control stationand during which, e.g.,- at the end of period 4, the multivibrator CY,CX, at the control station returns to mark to operate one or other ofrelays CP, CN. At the end of period 5, relay SS at the remote station isenergized. The connections and operation of contacts sp3 .9212 are suchthat the resulting operation of contact .954 always causes a change ofsignalling conditions at point A, which change is used to initiate acycle of the multivibrator CY, CX at the con-' trol station. At the endof the third period 6, contact ss4 is restored. If the next signal to betransmitted is the same as the last, as is the case if both bankcontacts 1, 2; when tested are found in the same condition, therestoration of contact SS4 causes a further change in the signallingcondition applied to the point A. On the other hand, if the bankcontacts were not in the same condition, the restoration of contact ss4does not cause a change of signalling conditions at point A. It is to beunderstood that the division of a signal into equal time periods wasmade arbitrarily and for ease of description and is not essential.Thevtwo essential features of a signal are, firstly, an information timeperiod during which either of two alternative signalling conditions isapplied for transmission and, secondly, a change-over in signallingconditions. The direction of the change-over is not important, that isto say it may be either from a first to a second signalling condition,or from the second to the first condition. Neither is it of importancewhether the information time period of a signal precedes or follows thechange-over provided the circuits of the transmitter and receiver aresuitably designed. In order that the same signalling condition may beapplied during the information time period of successive signals, asignalmay contain a second change of signalling conditions, e.g., at theend of thepen' d 6 in the signals 4, 5, 6, in addition to the twoessential features mentioned.

In FIGS. 1, 2,,a1l relays with more than one winding are shown in themark condition, the arrows indicating the direction of flow of markingcurrent in the individual windings. Single-winding relays are shown inthe released condition. When noinf ormation is being transmitted, relayCP is energized and its contactsare in the opposite positions to thoseshown, while the contacts of other relays are in the positionsindicated. When no information is being transmitted, each ofthemultivibrators is held inoperative by an inhibiting current flowingin its third winding. At the control station, this current alsoenergises relay CP. r In FIGS. 3, 4, a shaded area represents a lapse oftime during whicha piece of equipment, such as a relay, a key oracontact, is in a condition other than that depicted in FIGS. 1, 2. Forthe purposes of description, it will be assumed that the supervisorycontact SUPS' (FIG. 2) has been closed before the commencement of theoperations to be described. It will also be assumed that the supervisorycontacts connected to the other bank contacts of the uniselector SW arevall open. f

.To initiatethe transmission of supervisory information, the control keyat the control station is thrown, applying negativebattery to line.Thereafter the following operations occur in the time periods indicated,

. 8 the time periods being numbered in accordance with FIGS. 3, 4.

Time period 0 Remote station.-Relay SR operates to space and remains atspace so long as the control key is thrown. Contact srl opens,interrupting the inhibiting current flowing in the third winding ofrelay SY. The multivibrator, consisting of relay SY and its followerrelay SX, is released, changing to space and starting to run freely.With contact sx1 at space, relay SS is energized, closing contact ssland energizing the drive magnet of the uniselector SW. The uniselectorSW, however, does not step, being of the type which steps on the releaseof the driving magnet. When relay SS is energized, contact ss4 changesover, changing the signalling condition at point A from negative overcontact sp3 to positive over contact sn2. I

Control station.-Relay CR changes to space in response to the change insignalling condition at point A. In moving from mark to space, contactcr1 interrupts the inhibiting current through the third winding of relayCY. Relay CY, followed by relay CX, changes to space. The change-over ofcontact crl also releases relay CP. By the time contact cr1 has moved tospace and contact cp3 has closed, contact cxl has moved to space. Whencontact cpl has closed, the slow-to-release guard relay CG is energized.The slow release facility enables the relay CG to remain operated duringperiods when Time period 1 Remote station-This period is initiated whenthe multivibrator SY, SX returns to mark of its own accord. The openingof contact 'sxl releases relay SS. The opening of contact ssl releasesthe. drive magnet of the uniselector SW which steps to bank contact 1.The restoration of contact ss4 changes the signalling condition at pointA from positive over contact sn2 to negatlve over contact sp3.

Control station.-Relay CR changes to mark in response to the change insignalling condition at the point A. Contact crl, in moving to mark,prepares 'a circuit for the operation of relay CP.

Time period 2 Remote station.The conditions estaiblished during timeperiod 1 are maintained unchanged.

Control stati0n.The period is initiated when the multivibrator CY, CXreturns to mark of its own accord. For ease of description, the returnto mark is regarded as takingplace in the middle of the combined period1-2 However, the return may take place at any convenient time'afterrelay CR has had time to operate. When the multivibrator returns tomark, contact cxl moves to mark. Current then flows over contact cxl atmark, through the third winding of relay CY, over contact crl at mark,contact 0113 and then through relay CP. This current inhibits-themultivibrator, which is therebyheld in the mark condition. The curerntalso energizes relay CP. Contact cpl opens, but relay CG, being slow torelease, remains operated until this contact closes again. Withcontactcgl operated, the closing of contact cpl energlzes' the driving magnetof the uniselector CW. The uniselector CW, however, does not step, beingof the type which steps on the release of the driving magnet.

Time period 3 Remote stati0n.-This period is initiated when themultivibrator SY, SX. changes to space of its own accord. As before,relay SS and magnet SW are energized. The closing of contact ss2 testsbank contact 1 on-which the uniselector SW is now standing. Since thesupervisory contact connected to this bank contact'is open,

relay SP does not operate. The closing of contact ss 3 prepares a holdcircuit for relay SN, which however is Time period 4,

Remote station.This period is initiated when the multivibrator SY, SXreturns to mark of its own accord- As before, relay SS is released,magnet SW is deenergized, and the uniselector SW steps to bang contact2. This con tact,.however, is not tested until contact ssZ is closed intime. period 6.

The restoration of contact ss4 applies to point A a signalling conditiondependent. on the position of, contact .rp3, which in turn is determinedby whether or not relay SP was operated when bank contact 1 was tested.Since, however, relay SP was not operated, the restoration of contactss4 changes the signalling condition from positive over contact m2 tonegative over contact sp3.

Control stalion.-Relay CR changes to mark in response to the change insignalling conditions at point A. As before, contact crl, in moving tomark, prepares a circuit for the operation of relay CP.

Time period 5 Remote station-The conditions established during timeperiod 4 are maintained unchanged.

Control station.The period is initiated when the multivibrator CY, CXreturns to mark of its own accord. As before, the multivibrator isinhibited and relay CP is energized. The closing of contact cp2energizes the drive magnet CW over contact cgl operated. Since contactand is not operated, relay CIA. (not shown, but which is connected tobank contact 1 in the same way as relay C3A is connected to bank contact3) is not energized. Consequently its contact c1a2 (not shown, but whichis connected similarly to contact c3a2) is not operated. Hence, thegreen lamp corresponding to bank contact It continues to glow.

Time period 6 Remote station.-This period is initiated when themultivibrator SY, SX changes to space of its own accord. As before,relay SS and magnet SW are energized. Relay SP does not operate, sinceit is assumed that the supervisory contact connected to bank contact 2,on which the uniselector SW is now standing, is open. When contact SS4changes over, the signalling condition at point A is changed fromnegative over contact spS to positive over contact sn2.

Control. station-Relay CR changes to spacein response to the change. insignallingconditionat point A. As before, the change-over of contact crldeenergizes relay CP, and release the multivibrator which moves tospace. The opening of contact. cpZ, as previously, deenergizes the drivemagnet of the uniselector CW which steps to bank contact 2.

Time period 7 Remote station.This period is initiated when themultivibrator SY, SX returns tomark of its own accord. As before, relaySS is released. The uniselector SW steps to bank contact 3. With thesupervisory contact SUP3 assumed closed, positive battery appears onbank contact 3, but this is ineffective at this stage since contact mlis not operated. Since relay SP was not operated when bank contact 2 wastested, the restoration of contact m4 changes the signalling conditionat point A from negative over contact sp3 to positive over contact m2.

Control station.Relay CR changes to mark in response to the change insignalling conditions at point A. As before, contact crl, in moving tomark, prepares a circuit for the operation of relay CP.

Time period 8 Remote station.The conditions established during timeperiod 7 are maintained unchanged.

Control station.-The period is initiated when the multivibrator. CY, CXreturns to mark of its own accord. As before, the multivibrator isinhibited and relay CP and the drive magnet CW are energized. The greenlamp corresponding to bank contact 2 continues to glow.

Time period 9 Remote station.This period is initiated when themultivibrator SY, SX changes to space of its own accord. As before,relay SS and magnet SW are energized, and thechange-over ofcontact ss ichanges the signalling condition at point A from negative over contactspS to positive over contact 5112. With the uniselector SW standing onbank contact 3, the operation of contact ss2 causes relay SP to beenergized, since supervisory contact SUP3.

is assumed closed. The closing of contact spl prepares a hold circuitfor relay SP. The closing of contact sp2 prepares an operating circuitfor relay SN. The changeover of contact sp3 prepares the connection ofpositive battery to point A in time period. 19.

Control station.As before, relay CP changes to space in response to thechange of signalling conditions at the point A. As before, thechange-over of contact crl deenergizes relay CP, and releases themultivibrator which moves to space. As before, the drive magnet CW isreleased. The uniselector CW steps to bank contact 3.

Time period 10 Remote station.This period is initiated when themultivibrator SY, SX returns to mark of its own accord. As before, relaySS is released. This time, the restoration of contact .rs4 does notcause a change in signalling conditions at point A, since, this time,contact sp3 is operated. With contact sp3 operated and contact s54restored, positive battery is connected to point A during time periods10, 11, which together constitute the information time period of thesignal relating to bank contact 3. The opening of contact ssldeenergizes the magnet of theuniselector SW which steps to bank contact4. The restoration of contact SS2 completes a hold circuit for relay SPover its own contact spl operated. On the restoration of contact ss3,relay SN is energized over contact sp2 operated. The closing of contactsnl prepares a hold circuit for relay SN. The change-over of contact m2ensures a change of signalling conditions at point A when relay SS isnext operated and contact ss4 changes over at the beginning of timeperiod 12.

Control station.-Since there was no change in signalling conditions atpoint A, the conditions of time period 9 are maintained unchanged. Inparticular, relay CR and its contact crl remains at space, therebypreparing a circuit for the operation of relay CN instead of relay CP.

Time period 11 Remote station-The conditions established during timeperiod 10 are maintained unchanged.

Control stati0n.-The period is initiated when the multivibrator CY, CXreturns to mark of its own accord. As before, when contact cxl returnsto mark, the multivibrator is inhibited by current flowing through thethird Winding of relay CY. This time, since contact crl is at space,relay CN is operated in series with the third winding of relay CY. Thedrive magnet CW is energized over contacts cnZ, cgl both operated. Withthe uniselector CW standing on bank contact 3 and with contacts c114,cgZ both closed, relay C3A is energized in series with resistor R3.Relay C3A locks in series with its own contact c3ali operated andresistor R3. The change-over of contact 05oz extinguishes the green lampcorresponding to bank contact 3 and lights the corresponding red lamp.

Time period 12 Remote station-This period is initiated when themultivibrator SY, SX changes to space of its own accord. As before,relay SS and magnet SW are energized. The change-over of contact ss4changes the signalling condition at point A, this time, from positiveover contact sp3 operated to negative over contact snZ operated. Withthe uniselector SW now standing on bank contact 4, the operation ofcontact s52 breaks the hold circuit for relay SP over contact spl. Theoperation of contact ss3 completes a hold circuit for relay SN. Therelease of relay SP restores contacts spl, sp2, sp3.

Control statz'0n.In response to the change of signalling conditions atpoint A, relay CR changes, this time, from space to mark. Thechange-over of contact crl deenergizes relay CN and releases themultivibrator which moves to space. The opening of contact cn2deenergizes the drive magnet of the uniselector CW which steps to bankcontact 4.

Time period 13 Remote statz'0n.This period is initiated when themultivibrator SY, SX returns to mark of its own accord. As before, relaySS is released. This time, the release of contact ss4 does not cause achange of signalling conditions at A, negative battery being appliedbefore the release over contact sn2 (operated since time period 10) andafter the release over contact sp3 (restored in time period 12). Theopening of contact ssl results in the uniselector SW stepping to bankcontact 5. The restoration of contact ssz is ineffective since relay SPwas released in time period 12. The restoration of contact ss3 breaksthe hold circuit for relay SN which releases.

Control stati0n.-As there is no change in signalling condition at pointA, relay CR is not operated and re mains at mark. The conditionsestablished during time period 12 are maintained unchanged.

Time period 14 Remote statz'0n.The conditions established during timeperiod 13 are maintained unchanged.

Control stazi0n.The period is initiated when the rnultivibrator CY, CXreturns to mark of its own accord. As before, when contact 0x1 moves tomark, the multivibrator is inhibited and relay CP is energized.

Time period 15 onwards Remote stati0n.-Time period 15 is initiated whenthe multivibrator SY, SX changes to space of its own accord. Thechange-over of contact ss4 changes the signalling condition at point Afrom negative over contact sp3 (restored in time period 12) to positiveover contact sn2 (restored in time period 13). Thereafter the actioncontinues in the manner already described.

Control stati0n.As before, relay CR changes to space in response to thechange of signalling conditions at point A. Thereafter the actioncontinues in the manner already described.

Both stati0ns.The action just described is repeated until control key atthe control station is restored. When this occurs, relay SR is operatedto mark. The movement of contact srl to mark is ineffective at thisstage, since wiper swl is not standing on bank contact 0. Themultivibrator SY, SX continues to operate and the uniselector SWcontinuesto step, as do similarly the multivibrator CY, CX and theuniselector CW, until the uniselector SW steps on to bank contact 0.When this occurs, inhibiting current flows over contact sr1 at mark,wiper swl and the third winding of relay SY. The multivibrator SY, SKand the uniselector SW come to rest. At the control station, inhibitingcurrent flows through the third winding of relay CY in series with relayCP (or CN) as already described. The operation of the multivibrator CY,CX is inhibited, but the uniselector CW is one bank contact behind theuniselector SW. However, the continued energization of relay 0? (or CN)holds contact cpl (or cnl) open and relay CG is released. Contact cglrestores and completes a homing circuit for the uniselector CW whichincludes the drive magnet CW, the make and break contact mb and thethird bank of uniselector CW having a common bank contact for all bankcontacts of the other banks (CW1 and CW2) except the home contact 0.When wiper cw3 steps on to bank contact 0, the uniselector-CW comes torest.

Second cycle Now suppose that the supervisory contact SUP3 is openedbefore the control key is operated for the second time. Under theseconditions, when bank contact 3 is tested by the uniselector SW, relaySP will not operate. The signal relating to bank contact 3, will consistof an information time period (time periods 10, 11) in which, this time,negative battery is applied topoint A, together with a change insignalling conditions at the beginning of time period 12. There willalso, this time, be a second change in signalling conditions at thebeginning of time period 13. At the control station, the relay CN will,this time, not be operated during the information time period of thesignal for bank contact 3. Relay CP, however, will be operated in themanner already described. The closing of contact cp4 completes a shortcircuit for relay C3A. The short circuit includes contact c3a1 operated,wiper cwl, contacts cgZ, cp4 both operated, wiper cw2 and resistor R3.Relay C3A releases. The opening of contact c3a1 breaks the circuit bywhich relay C3A was held operated. The restoration of contact c3a2extinguishes' the red lamp corresponding to bank contact 3 andlights'the corresponding green lamp. Thereafter the action is as alreadydescribed.

While the principles of the invention have been described above inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationon the scope of the invention.

What we claim is:

1. An electric signal system comprising:

a transmitter to generate a transmission signal including at least oneinformation time period having at least one information signal portionand another information signal portion in sequence, said transmitterincluding a source of voltage having two output terminals, one of saidoutput terminals providing a first voltage level and the other of saidoutput terminals providing a second voltage level distinct from saidfirst voltage level,

a first switching means selectively coupled to said two output terminalsto produce at the output of said first switching means at least a firstchange between said first voltage level and said second voltage level assaid one information signal portion, and

a second switching means selectively coupled to said two outputterminals to select one of said first voltage level and said secondvoltage level for coupling to said output of said first switch- 13* ingmeans as, said another information signal portion;

a transmission medium coupled to said output of said first switchingmeans for propagation of said transmission signal; and a receiverincluding a third switching means coupled to said transmission mediumresponsive to said first change of said oneinformation signal portionand said l t d one f id. first voltage level and said in sequence withsaid one information signal portion second voltage level of said anotherinformation including a selected one of said first voltage level signalportion of said transmission signal for andlsaid second voltage level;operation thereof, a switching means coupled to said transmission mediumtwo means each representingv one of said first voltresponsive tosaidfirst change of saidv one informaagelevel and said second voltagelevel coupled 15 tion signalv portion and-said selected one of saidfirst to said third switching means for exclusive sevoltage level andsaidsecond voltage level of said l i f oneof id t means by said thirdanother information signal portion of said transmismeans during theoperationthereof, and sion signaltfor operation thereof; energizingmeans coupled to said third switching two means each representing one ofsaid first voltage means to activate the selected one of said two leveland said second voltage level coupled to Said means. 2. An electricsignal transmitter togeneratea transmisswitching meanslfor exclusiveselection of one of said two meansby said switching means duringoperation thereof; and

sion signal including at least one information time period having atleast one information signalportionandanotherainforrnation. signalportion in sequence comprising:

energizing means coupled to said switching means to activatetheselectedone of said twomeans.

a source of voltage having two output terminals, one of said outputterminals providing a first; voltage level and the otherof said outputterminals providinga second voltage level distinct from saidfirst volt-6. A receiver according to claim 5, wherein said transmissionsignalincludes in said one information signal portion a second changebetween said first voltagelevel and said second voltage,level;

age level; said switching means is responsive to said first changeafirst switching means selectively coupled'to said two in said oneinformation signal por iO to initiate output terminals to produce at theoutput of said p ati n thereof; first switching me-ans at least a firstchange between Said energizing means includes said first voltage leveland said second voltage level a delay device coupled to Said W C iHg mans i i fo atio i l i activated by said switching means uponthe iniasecond; switching-means selectively coupled to said tiation of Operatienthereof to pr vide a pretwo output terminals to select one of-said firstvoltage determined time delay before Said selecifid one level and saidsecond voltagerlevel for coupling to of Said tWO means is activated ySaid energizing said output of said first switching means as said 40 j rd another i f ti i 1 i d said switching means responds to said secondchange atransmission medium coupled to said output. of said durmg aidpredetermined time delay to Selfict the first switching means forpropagation of saidtrans p p i 0116 f said two means. mission i L 7. Areceiver according to claim 6, wherein A transmitter. according to l i 2wherein said transmission signal includes in sequence a plurality saidfirst switching means; produces at said output of qm o r time P and saidfirst switching means a third information signal Sald recelver furthe rportion for said information time period in sequence a phirahtyindicators F R f g f with said one and said another information signalsald plulahty of 5315 Information tlme penods portions including asecond change between said first two s g i States cone volta e level andsaid second voltage level; and g 0 one o Sal rs v0 tage level i a V tsaid second voltage level and the other of said said second switchingmeans remain inoperative to set t corresponding to the. other offsaidfirst lect a g l one of Bald s Voltage levfil and, f voltage, level andsaidsecond voltage level; and second voltage level as d anotherlnformatlon a distributor coupled tosaid two means andsaid plusignalportion. 55, rality of indicators controlled by the repetitious oper- 4.A transmitter according to Claim 2, f rth r incl g ation-of-said delaydevice to sequentially engage each testing means coupled to said secondswitching means of said indicators, the state of any one of said indifortesting in sequence the condition of each of a gators being; determinedby which of said two means plurality of test terminals to operate saidsecond 9 I d 8 the Period of engagement y Said switching means inaccordance with the condition of dlsmbutoli the successive testterminals tested; An elfjctrlQslgnal system Comprising: driving meanscoupledto said first switching means and a trans-utter mcludmg Saidtesting means to control the sequential testing a firstymonostable relaymultivibrator activated 1n of said testing means; and msponse to acontrol slgnail; said first and second switching means cooperate to acoptrol relay (lollpled to sand f multlvlbratpr said first multivrbratorcontrolling the operating generate said transmission signal having insequence condition of Said control gala v l y, a plurahty of sa dinformation time periods, each of a first u ms 61E ct ,Said F P- timelieriods, including Said one a first contact controlled by said controlrelay Information slgna-l-portlon Sald first change and the coupled tosaid first uniselector to successively presence or absence of a secondchange between said firstvoltage level and said second voltage level asdetermined by the condition of said test terminal previously tested, andas said second information period one-of said first voltage level andsaid second testthe condition of a plurality of devices;

first and second test relays;

a source of'voltage having two outputs, eachoutput providing a differentvoltage level, one of said voltage levels providing a first signalling15 7 condition and the other of said voltage levels providing a secondsignalling condition, a second contact controlled by said first testrelay to be selectively connected to said outputs of 1 6 a control relaycoupled to said multivibrator, said multivibrator controlling theoperating condition of said control relay; a testing uniselector;

said source of voltage; a first contact controlled by said control relaycoupled a third contact controlled by said second test relay t0 saiduniselector t0 successively test the condition to be selectivelyconnected to said outputs of of aplurality 0f (latices; id o r f v ltfirst and second test relays;

fourth and fifth contacts controlled by said control a source of voltageh g two p each output relay interconnecting said first uniselector and10 Providing a difiefent l g levfil, one of Said Voltboth s id te trelays t r d r aid t t relays age levels providing a first signallingcondition and responsive to the condition of the device tested the otherof Said Voltage levels Providing a Second by said first uniselector;signalling condition;

s a tran is i dium; d a second contact controlled by said first testrelay to a ixth contact nt ll d b s id t l relay to be selectivelyconnected to said outputs of said source be sequentially coupled to saidsecond and third 0f tag contacts to u l t aid tr i i n di a thirdcontact controlled by said second test relay to a transmission signalhaving a duration equal to be selectively connected to said outputs ofsaid source the energization-deenergization cycle of said conof g trolrelay including a first change between said fourth and fifth contactscontrolled by said control refi t d second signalling diti upon rlayinterconnecting said uniselector and both said gization f id t l l one fid fi t test relays to render said test relays responsive to theandsecond signalling conditions as determined condition of the devicetested by said uniselector; by the condition of the device tested bysaid first a a smission medium; and i l t d th presence or absence f a asixth contact controlled by said control relay to he seemd changebetween said first and second sequentially coupled to said second andthird COI1- signalling conditions as determined by the contacts tosupply to said transmission medium a transdition of the devicepreviously tested by said first s n Signal having a duration q l to the6116f uniselector upon deenergization of said control a Il- 'g Cycle ofSaid Control relay relay; and eluding a first change between said firstand second a receiver coupled to said transmission medium includingswitching means having two contacts responsive to said transmissionsignal;

a first relay coupled to one of said contacts of said switching means;

a second relay coupled to the other of said contacts of said switchingmeans; 7

a second monostable relay multivibrator including signalling conditionsupon energization of said control relay, one of said first'and secondsignalling conditions as determined by the-condition of the devicetested by said uniselector and the presence or tabsenee of a secondchange between said first and second signalling conditions as determinedby the condition of the tested previouslytested upon deenergization ofsaid control relay.

11. A transmitter according to claim 10, wherein said control signal foractivating said multivibrator is received atsaid transmitter from aremote location over said transmission medium.

12 An electric signal receiver comprising:

swltehing means having two outputs responsiveto received signalsincluding information in the form of one of two distinct signallingcondition and at least one change between said two signalling conditlonsto select one of said two outputs in accordance with which of said twosignalling conditions is presinhibiting winding coupled to saidswitching 40 means responsive to said first change of said transmissionsignal to render said second multi vibrator operative and to select oneof said two contacts of said switching means in accordance with which ofsaid first and second signalling conditions is present;

a seventh contact controlled by said second multivibrator in series withsaid inhibiting winding, said seventh contact closing after a delaydetermined by the operating time of said second mulout; w tivibrator toestablish a connection for an ina first relay coupled to one of saidoutputs; hibiting current through said inhibiting winding, 21 secondrelay coupled to the other of said outputssaid switching means and oneof said first and a monostable relay multivibrator including an i hibisecond relays depending upon which of said ing winding coupled to saidSwitching means.

contacts of SE11d SW1ECh1I1g means 15 Selected to a contact controlledby said multivibrator in series with gneder one of'sard first and secondrelays op said inhibiting winding, said contact closing after a a seconduniselector including a plurality of consgg g i i g g 'operanilg tune ofi t1- tacts coupled to said first and second relays; r 0 es a i i t i-lfl i means coupled to said first and second relays and .Current throughsmd i' Sald swltch' said second uniselector to step said second unimgmeans and of first and Second Telays pending upon WhlCh of said outputsis selected;

selector sequentially to each of said plurality of contacts at eachinterruption of Said inhibiting a uniselector includmg a plurality ofcontacts coupled to said first and second relays;

current; and a plurality of indicators each coupled to one of said r'means coupled to said first and Second relays and said 60 plurality ofcontacts of said second uniselector uniselector to step said uniselectorsequentially to operable to one of two states in accordance with each ofsaid plurality of contacts at each interruption whlchof said first andsecond relays 1s rendered of said inhibiting current caused by saidchange beoperative. tween said two signalling conditions; and

y f accofdmg to m 8, Wherem f a plurality of indicators each coupled toone of said trol signal is transmltted from said receiver to saidtransplurality of contacts operable to one of ttwottates nutter Oversaldfraflsmlsslon in accordance with which of said first and second 10.An electric signal transmitter comprising: relays is rendered operativea monostable relay multivibrator activated in response to acontrolsignal; (References on following page) References Cited by the ExaminerUNITED STATES PATENTS Nyquist 340-170 XR Rasmussen 1718-70 Potts 178-70Schaefer 340-203 Thomson 340-167 Place 340-172 Taylor et a1 340-226 XCornu 340-226 Purington 340-167 Neiswinter 340-226 18 Brown 340-348Tolsom 340-183 X Barber 340-170 Ingham 178-67 Kuehl 340-348 Hawley 340-226 X Warnock 340-170 Brosh 340-226 X 10 NEIL C. READ, Primary Examiner.

EVERETT R. REYNOLDS, IRVING L. SRAG'OW,

Examiners.

1. AN ELECTRIC SIGNAL SYSTEM COMPRISING: A TRANSMITTER TO GENERATE ATRANSMISSION SIGNAL INCLUDING AT LEAST ONE INFORMATION TIME PERIODHAVING AT LEAST ONE INFORMATION SIGNAL PORTION AND ANOTER INFORMATIONSIGNAL PORTION IN SEQUENCE, SAID TRANSMITTER INCLUDING A SOURCE OFVOLTAGE HAVING TWO OUTPUT TERMINALS, ONE OF SAID OUTPUT TERMINALSPROVIDING A FIRST VOLTAGE LEVEL AND THE OTHER OF SAID OUTPUT TERMINALSPROVIDING A SECOND VOLTAGE LEVEL DISTINCT FROM SAID FIRST VOLTAGE LEVEL,A FIRST SWITCHING MEANS SELECTIVELY COUPLED TO SAID TWO OUTPUT TERMINALSTO PRODUCE AT THE OUTPUT OF SAID FIRST SWITCHING MEANS AT LEAST A FIRSTCHANGE BETWEEN SAID FIRST VOLTAGE LEVEL AND SAID SECOND VOLTAGE LEVEL ASSAID ONE INFORMATION SIGNAL PORTION, AND A SECOND SWITCHING MEANSSELECTIVELY COUPLED TO SAID TWO OUTPUT TERMINALS TO SELECT ONE OF SAIDFIRST VOLTAGE LEVEL AND SAID SECOND VOLTAGE LEVEL FOR COUPLING TO SAIDOUTPUT OF SAID FIRST SWITCHING MEANS AS SAID ANOTHER INFORMATION SIGNALPORTION; A TRANSMISSION MEDIUM COUPLED TO SAID OUTPUT OF SAID FIRSTSWITCHING MEANS FOR PROPAGATION OF SAID TRANSMISSION SIGNAL; AND ARECEIVER, INCLUDING A THIRD SWITCHING MEANS COUPLED TO SAID TRANSMISSIONMEDIUM RESPONSIVE TO SAID FIRST CHANGE OF SAID ONE INFORMATION SIGNALPORTION AND SAID SELECTED ONE OF SAID FIRST VOLTAGE LEVEL AND SAIDSECOND VOLTAGE LEVEL OF SAID ANOTHER INFORMATION SIGNAL PORTION OF SAIDTRANSMISSION SIGNAL FOR OPERATION THEREOF, TWO MEANS EACH REPRESENTINGONE OF SAID FIRST VOLTAGE LEVEL AND SAID SECOND VOLTAGE LEVEL COUPLED TOSAID THIRD SWITCHING MEANS FOR EXCLUSIVE SELECTION OF ONE OF SAID TWOMEANS BY SAID THIRD MEANS DURING THE OPERATION THEREOF, AND ENERGIZINGMEANS COUPLED TO SAID THIRD SWITCHING MEANS TO ACTIVATE THE SELECTED ONEOF SAID TWO MEANS.